Graphite material and preparation method therefor, negative electrode sheet, battery and electric device

Abstract

Disclosed in the present application are a graphite material and a preparation method therefor, a negative electrode sheet, a battery, and an electric device. The graphite material comprises a graphite core and a coating layer, wherein the graphite core is filled with a filler.

Description

A graphite material and its preparation method, a negative electrode, a battery, and electrical equipment thereof.

[0001] This application claims priority to Chinese Patent Application No. 202510022003.3, filed on January 6, 2025, entitled "A graphite material and its preparation method, negative electrode sheet, battery and electrical device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of electrochemical technology, specifically relating to a graphite material and its preparation method, a negative electrode, a battery, and electrical equipment. Background Technology

[0003] Graphite, as an important component of lithium-ion batteries, has the advantages of large reserves and low cost. However, its high interlayer spacing leads to large expansion during charging and discharging. The stress generated by the expansion during cycling can cause the graphite sheets to detach, resulting in accelerated capacity decay. At the same time, graphite particles have abundant internal pores and large surface defects, making them prone to side reactions at high temperatures. All of these factors limit the use of graphite as a negative electrode material. Summary of the Invention

[0004] To at least solve one of the technical problems existing in the prior art, this application provides a graphite material and its preparation method, a negative electrode sheet, a battery, and an electrical device.

[0005] The first aspect of this application provides a graphite material comprising a graphite core and a coating layer, wherein the graphite core is filled with a filler.

[0006] The applicant of this application discovered that untreated graphite materials possess a rich porous structure and a large specific surface area. Filling with a filler can reduce the specific surface area of ​​graphite materials, thereby improving their high-temperature performance. Simultaneously, coating the surface of the graphite core can alleviate the cyclic expansion effect of graphite materials, facilitating lithium-ion transport and lowering the diffusion barrier of lithium ions at low temperatures. By filling the graphite core and coating the graphite material, the internal porosity and external structure of the graphite material can be optimized. The graphite material provided in this application exhibits excellent low-temperature rate performance, high-temperature storage performance, and cycling performance, catering to applications under both high and low temperature conditions.

[0007] The second aspect of this application provides a method for preparing a graphite material as described in the first aspect, comprising the following steps: mixing a graphite precursor and a filler to obtain a graphite core precursor; subjecting the graphite core precursor to a first high-temperature treatment to obtain a graphite core; and mixing the graphite core and a coating agent to a second high-temperature treatment to obtain a graphite material.

[0008] The method for preparing graphite materials provided in this application is simple, easy to operate, has low energy consumption, and is easy to mass-produce.

[0009] A third aspect of this application provides a negative electrode sheet, comprising the graphite material described in the first aspect or the graphite material prepared by the preparation method described in the second aspect. The negative electrode sheet comprising the graphite material of this application can accommodate applications of the negative electrode sheet under both high and low temperature conditions.

[0010] A fourth aspect of this application provides a battery including the negative electrode sheet described in the third aspect. The battery includes a negative electrode sheet using the graphite material described in this application, which can balance the battery's low-temperature and high-temperature performance.

[0011] A fifth aspect of this application provides an electrical device including the battery described in the fourth aspect. The electrical device, including the battery using the graphite material of this application, thus exhibits excellent low-temperature and high-temperature performance. Detailed Implementation

[0012] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0013] This application provides a graphite material comprising a graphite core and a coating layer, wherein the graphite core is filled with a filler.

[0014] Specifically, untreated graphite materials possess a rich porous structure and a large specific surface area. Filling with fillers can reduce the specific surface area of ​​graphite materials, improving their high-temperature performance. Simultaneously, coating the graphite core with a coating layer can mitigate the cyclic expansion effect of graphite, facilitating lithium-ion transport and lowering the lithium-ion diffusion barrier at low temperatures. By filling the graphite core and coating the graphite material, both the internal porosity and external structure can be optimized. The graphite material provided in this application exhibits excellent low-temperature rate performance, high-temperature storage performance, and cycling performance, catering to applications under both high and low temperature conditions.

[0015] According to some embodiments of this application, the filler includes one or more of asphalt, coal tar, and heavy oil, and / or the coating layer includes one or more of asphalt, hard carbon, heavy oil, glucose, starch, and resin.

[0016] Specifically, the filler is selected from one or more of the above-mentioned materials and can fill into the interior of the graphite core, reducing the porosity of the graphite material, thereby reducing the specific surface area of ​​the graphite material, and improving the structural stability and lifespan of the graphite material. The coating layer is selected from one or more of the above-mentioned materials and can effectively coat the surface of the graphite material. The coating effect is good, resulting in a larger interlayer spacing between the graphite materials, which is beneficial to lithium-ion transport and reduces the diffusion barrier of lithium ions at low temperatures. At the same time, it reduces the direct contact between the electrolyte and the graphite material, reducing the occurrence of side reactions. In some embodiments of this application, the resin may include epoxy resin, phenolic resin, organic resin, and liquid-phase resin, etc.

[0017] According to some embodiments of this application, the covering layer includes at least two covering structures.

[0018] Specifically, graphite materials have a multi-layered coating structure, which can improve the coating effect of graphite materials and further improve the low-temperature performance of batteries.

[0019] According to some embodiments of this application, the coating layer includes an inner coating structure close to the graphite core and an outer coating structure away from the graphite core, wherein the material of the inner coating structure is the same as the material of the filler.

[0020] Specifically, in one embodiment of this application, the graphite material includes a two-layer coating structure, comprising an inner coating structure close to the graphite core and an outer coating structure away from the graphite core. The material of the inner coating structure is the same as the material of the filler. By using a filler to fill and coat the graphite material, the coating effect of the graphite material can be improved, the coating uniformity of the graphite material can be enhanced, and the occurrence of side reactions can be reduced.

[0021] In another embodiment of this application, the graphite material includes a three-layer coating structure: an inner coating structure close to the graphite core, an outer coating structure away from the graphite core, and an intermediate coating structure located between the inner and outer coating structures. The material of the inner coating structure is a filler, and the materials of the intermediate and outer coating structures can be coating agents, specifically resin and asphalt. More specifically, the positions of the resin and asphalt are not specifically limited. The material of the intermediate coating layer can be resin, and the material of the outer coating layer can be asphalt, or the material of the intermediate coating layer can be asphalt, and the material of the outer coating layer can be resin.

[0022] According to some embodiments of this application, the graphite material satisfies: 0.15 ≤ BET*(I D / I G ) / OI≤0.4, where BET is the specific surface area of ​​the graphite material, I D / I GOI is the ratio of the intensity of the D peak and the G peak in the Raman spectrum of the graphite material, and OI is the ratio of the intensity of the (004) and (110) crystal plane diffraction peaks of the graphite material.

[0023] Specifically, the BET (Boiler Equivalent Temperature) of graphite materials is related to both their internal porosity and external defects, and the range of BET affects the high-temperature performance of graphite materials. D / I G It reflects the degree of defect in graphite materials and characterizes the degree of disorder on the surface of graphite materials; OI is the ratio of the diffraction peak intensities of the (004) and (110) crystal planes of graphite materials, characterizing the orientation of graphite. Through BET*(I D / I G The electrochemical reactivity of graphite materials can be characterized by a comprehensive reflection of their isotropy, internal pore size, and the degree of surface defects. D / I G The value of BET / OI can be, but is not limited to, 0.15, 0.18, 0.2, 0.25, 0.3, 0.35, 0.4, etc. Specifically, BET*(I D / I G By controlling the π / OI ratio within the range of 0.15 to 0.4, the internal pores and external structure of graphite materials can be optimized, reducing the probability of side reactions and improving the high-temperature performance. Simultaneously, it alleviates the cyclic expansion effect of graphite, which is beneficial for lithium-ion transport, lowers the diffusion barrier of lithium ions at low temperatures, and enhances the low-temperature performance of graphite materials. The graphite material provided in this application exhibits excellent low-temperature rate performance, high-temperature storage performance, and cycling performance, catering to applications under both high and low temperature conditions.

[0024] BET specific surface area test: Refer to the specific surface area test method specified in the national standard GB / T 24533-2019;

[0025] I D / I G Raman spectroscopy: Raman spectroscopy is used to characterize the degree of disorder in graphite materials. D 1350 cm⁻¹ in the Raman spectrum -1 Peak intensity at position, I G 1580cm -1 Peak intensity at position, peak intensity ratio I D / I G It reflects the degree of defects in the crystal lattice.

[0026] OI value test: The OI value of graphite material is tested to characterize its orientation. It is tested by X-ray diffraction. The OI value is calculated according to the following formula: OI = I(004) / I(110), where I(004) is the intensity of the diffraction peak of the (004) crystal plane of graphite material and I(110) is the intensity of the diffraction peak of the (110) crystal plane of graphite material.

[0027] According to some embodiments of this application, BET is 1.5m. 2 / g~5.0m 2 / g; and / or, I D / I G The value is 0.1 to 0.5; and / or, the OI is 2 to 5.

[0028] Specifically, the specific surface area of ​​graphite material is 1.5 m². 2 / g~5.0m 2 / g, due to the abundant porous structure inside graphite materials, untreated graphite materials have a relatively large specific surface area. Reducing the specific surface area of ​​graphite materials is beneficial to improving their high-temperature performance. BET can be, but is not limited to, 1.5m. 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g, 3.5m 2 / g, 4.0m 2 / g, 4.5m 2 / g, 5.0m 2 / g, etc.; I of graphite materials D / I G The value is 0.1 to 0.5, I D / I G The larger the graphite surface, the more defects it contains, providing more lithium insertion sites and channels for Li+, which helps accelerate the diffusion rate of lithium ions. D / I G The smaller the value, the better the cycle stability of the graphite material. D / I G Possible values ​​include, but are not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, etc.; the OI value of graphite materials ranges from 2 to 5. The smaller the OI value, the better the isotropy of the graphite material, the easier it is for Li+ to be transported, and the better the low-temperature power performance of the battery. OI values ​​can be, but are not limited to, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc. By comparing the BET and I values ​​of graphite materials... D / I G Within the above range, the better the isotropy of graphite materials, the better their cycle stability, and the faster the lithium-ion diffusion, which further improves the high-temperature and low-temperature performance of graphite materials.

[0029] According to some embodiments of this application, the electrochemically active area of ​​the graphite material is 1.5m². 2 / g~3.0m 2 / g. Specifically, the electrochemically active surface area of ​​graphite materials can be, but is not limited to, 1.5m². 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g. The electrochemical active area of ​​graphite materials refers to the surface area of ​​graphite materials that participates in electrochemical reactions. Within this range, the activity and efficiency of chemical reactions when graphite materials are applied to electrodes can be improved, thereby increasing the electrochemical reaction rate of the battery.

[0030] The electrochemical active area testing method is as follows: Assemble a coin-type lithium half-cell and perform AC impedance testing in a 298K constant temperature chamber. The test frequency range is 200kHz to 10mHz, and the excitation voltage is 5mV. By fitting the Nyquist curve, the electrochemical active area is determined using the formula... The electrochemical active area of ​​different types of graphite materials can be obtained.

[0031] Secondly, this application provides a method for preparing the graphite material described above, comprising the following steps:

[0032] S1: The graphite precursor and filler are mixed and processed to obtain the graphite core precursor;

[0033] According to some embodiments of this application, the graphite precursor includes one or more of artificial graphite and natural graphite. Natural graphite includes flake graphite, microcrystalline graphite, etc. The graphite precursor can be pretreated, such as by crushing, acid washing, drying, spheroidizing, etc., to obtain a graphite precursor with fewer impurities and a regular shape, which is beneficial for filling and coating.

[0034] According to some embodiments of this application, a graphite precursor and a filler are mixed and subjected to high-pressure treatment in a cold isostatic pressing apparatus. This allows the filler to fill into the graphite material, reducing the internal porosity of the graphite material, thereby reducing the specific surface area of ​​the graphite material and improving its high-temperature performance. Other methods may also be used in this application to fill the graphite core with the filler, and no specific limitations are made herein.

[0035] According to some embodiments of this application, the filler includes one or more of bitumen, coal tar, and heavy oil. The filler, selected from these materials, can fill and coat the interior and surface of graphite. In some embodiments of this application, while filling the graphite precursor with the filler, a coating layer can also be formed on the surface of the graphite precursor, further improving the pore structure of natural graphite. According to some preferred embodiments of this application, the filler is a liquid-phase filler, such as liquid heavy oil.

[0036] According to some specific embodiments of this application, the mass ratio of graphite precursor to filler is 100:(10-40). The mass ratio of graphite precursor to filler may include, but is not limited to, 100:10, 100:12, 100:15, 100:20, 100:25, 100:30, and 100:40. Within this range, the mass ratio of graphite precursor to filler can have a good filling modification effect.

[0037] S2: The graphite core precursor is subjected to a first high-temperature treatment to obtain the graphite core;

[0038] According to some embodiments of this application, the obtained graphite core precursor is subjected to a first high-temperature treatment to obtain a graphite core. The first high-temperature treatment includes high-temperature sintering, in which the obtained graphite core precursor filled with filler is sintered at high temperature, and a protective atmosphere can be introduced for protection to obtain the graphite core. The high-temperature sintering gives the graphite core a dense structure. During the sintering process, as the temperature rises, the volatile components in the filler gradually escape, forming a more ordered carbon structure inside the graphite material, so that the pores inside the graphite material are uniformly filled.

[0039] According to some embodiments of this application, the temperature of the first high-temperature treatment is 900℃ to 1500℃, and the duration of the first high-temperature treatment is 2h to 6h. When the temperature and time of the first high-temperature treatment are within the above range, the graphite core precursor can be carbonized more effectively, forming a more stable graphite core. Simultaneously, the pores inside the graphite precursor are filled, defects are further reduced, and the structure becomes more ordered. In some embodiments of this application, the temperature of the first high-temperature treatment can be, but is not limited to, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, etc.; the duration of the first high-temperature treatment can be, but is not limited to, 2h, 3h, 4h, 5h, 6h, etc.

[0040] According to some embodiments of this application, obtaining graphite cores by subjecting the graphite core precursor to a first high-temperature treatment further includes grinding the graphite cores (specifically, ball milling) and shaping them using a grinding device to eliminate the morphological changes caused by the aforementioned cold isostatic pressing, thereby obtaining near-spherical graphite cores from irregular particles. Specifically, the ball milling speed is 100 rpm to 800 rpm; the ball milling time is 2 h to 8 h. The ball milling speed and time are within the above range, which can change the morphology of the graphite material without damaging it, making it into near-spherical graphite particles, which is beneficial for subsequent graphite coating. In some embodiments of this application, the ball milling speed can be, but is not limited to, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, etc.; the ball milling time can be, but is not limited to, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, etc.

[0041] S3: The graphite core and coating agent are mixed and subjected to a second high-temperature treatment to obtain the graphite material.

[0042] According to some embodiments of this application, the coating agent includes one or more of asphalt, hard carbon, heavy oil, glucose, starch, and resin. The coating agent selected from one or more of the above materials can effectively coat the graphite core material and improve the structural stability of the graphite material. In some embodiments of this application, the coating agent can be applied to the graphite material with the filler coating layer to form a multi-layer coating layer. The multi-layer coating can improve the coating uniformity of the graphite surface, and the structure of the coating layer is more stable and less likely to crack or fall off due to expansion during cycling.

[0043] According to some embodiments of this application, the mass ratio of graphite core to coating agent is 100:(3-40). The mass ratio of graphite core to coating agent can be, but is not limited to, 100:3, 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, or 100:40. Within the above range, the mass ratio of graphite core to coating agent can have a better coating effect, repair graphite surface defects, and improve the disorder of graphite surface.

[0044] According to some embodiments of this application, the coating agent includes two or more coating agents, such as phenolic resin and asphalt. Using two or more coating agents can form a multi-layer coating, improving the coating effect on the graphite core, thereby improving the low-temperature rate performance of the battery. In some embodiments of this application, when phenolic resin and asphalt are used as coating agents, the mass ratio of graphite core, phenolic resin and asphalt can be, but is not limited to, 100:10:2.5, 100:10:5, 100:30:2.5, or 100:30:3.

[0045] According to some embodiments of this application, the second high-temperature treatment includes high-temperature sintering. The temperature of the second high-temperature treatment is 900℃ to 1500℃, and the treatment time is 2h to 6h. The purpose of the second high-temperature treatment is to form a coating layer on the graphite core material, alleviate the cyclic expansion effect of the graphite material, facilitate lithium-ion transport, reduce the diffusion barrier of lithium ions at low temperatures, and improve the low-temperature performance of the graphite material. In some embodiments of this application, the temperature of the second high-temperature treatment may be, but is not limited to, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, etc.; the treatment time may be, but is not limited to, 2h, 3h, 4h, 5h, 6h, etc.

[0046] Compared with the prior art, the method for preparing graphite materials provided in this application is simple, easy to operate, has low energy consumption, and is easy to mass-produce.

[0047] Thirdly, this application provides a negative electrode sheet comprising the graphite material described in the first aspect, or the graphite material prepared by the method described in the second aspect. The resulting negative electrode sheet exhibits excellent isotropy, high energy density, high initial charge-discharge efficiency, and good compatibility with the electrolyte.

[0048] According to some embodiments of this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). For example, the negative electrode current collector can be a copper foil.

[0049] According to some embodiments of this application, the negative electrode active material includes graphite material prepared by the method described in the first aspect or the method described in the second aspect, and may also include at least one of the following materials: soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc.

[0050] According to some embodiments of this application, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0051] According to some embodiments of this application, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0052] According to some embodiments of this application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, and binder, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes.

[0053] Fourthly, this application provides a battery including the aforementioned negative electrode sheet, which has excellent cycle performance and rate performance, while also maintaining a high energy density.

[0054] As an example, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, with the separator located between the positive and negative electrodes. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0055] According to embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material layer including a positive active material. The positive current collector can be a metal foil or a composite current collector (a composite current collector can be formed by depositing metal material on a polymer substrate), for example, the positive current collector can be aluminum foil.

[0056] In the embodiments of this application, the specific type of positive electrode active material is not particularly limited. As some specific embodiments, the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium cobalt phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium manganese oxide, binary materials, and ternary materials.

[0057] According to some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0058] According to some embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0059] According to some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, positive electrode lithium supplementation material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0060] According to some embodiments of this application, there are no particular limitations on the type of separator membrane; any known porous structure separator membrane with good chemical and mechanical stability can be selected. As an example, the material of the separator membrane may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitations. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitations.

[0061] According to some embodiments of this application, there are no specific limitations on the type of electrolyte, which can be selected according to requirements. According to some specific embodiments of this application, the electrolyte is an electrolyte solution, which includes a lithium salt and a solvent.

[0062] According to some specific embodiments of this application, lithium salts may include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonylimide (LiFSI), lithium phosphate (LiBOB), and lithium difluorophosphate (LiPO2F2).

[0063] According to some specific embodiments of this application, the solvent may include at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0064] In some embodiments of this application, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0065] Fifthly, this application provides an electrical device, which, according to an embodiment of this application, includes the battery described above. The features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0066] Specifically, the aforementioned electrical equipment can be, but is not limited to, electric vehicles, electric cars, mobile phones, tablets, laptops, electric toys, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0067] The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0068] The present application will be further described in detail below through examples.

[0069] Example 1

[0070] This embodiment illustrates the graphite material and its preparation method, negative electrode sheet, and battery disclosed in this application, and includes the following steps:

[0071] (1) Preparation of graphite materials:

[0072] Graphite precursors were obtained by crushing, acid washing, drying, and spheroidizing flake graphite. The graphite precursors and heavy oil filler were mixed uniformly at a mass ratio of 100:15 and processed using a cold isostatic pressing (CIP) machine at 100 MPa to obtain graphite core precursors. The graphite core precursors were then sintered at 1200℃ for 6 hours under N2 protection to obtain graphite cores. The graphite cores were then shaped using a ball mill at 200 r / min for 3 hours to eliminate the morphological changes caused by CIP, resulting in near-spherical graphite cores from irregular particles. Finally, the graphite cores were mixed with coating agent 1 (phenolic resin) and coating agent 2 (asphalt) at a ratio of 100:10:2.5 and sintered at 1200℃ for 4 hours under N2 protection. After sieving and demagnetization, the graphite material was obtained.

[0073] (2) Preparation of negative electrode:

[0074] The graphite material, conductive carbon black, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) prepared above were mixed in NMP at a mass ratio of 96.5:1:1.5:1 to form a homogenate. The homogenate was then coated onto a copper current collector, dried, rolled, and die-cut to obtain a negative electrode sheet.

[0075] (3) Preparation of the positive electrode:

[0076] Lithium iron phosphate, carbon nanotubes, and polyvinylidene fluoride (PVDF) were mixed in NMP at a mass ratio of 100:3:2 to form a slurry. The slurry was then coated onto an aluminum current collector, dried, rolled, and die-cut to obtain a positive electrode sheet.

[0077] (4) Battery fabrication:

[0078] The positive electrode, separator, negative electrode and electrolyte prepared above are assembled to prepare a full cell; a solution of LiPF6+EC:DEC:DMC (volume ratio of 1:1:1) with appropriate additives is used as the electrolyte and a polypropylene membrane is used as the separator.

[0079] Example 2-14

[0080] Examples 2-14 are basically the same as Example 1, except that the preparation of graphite materials is different. For specific parameters, please refer to Table 1.

[0081] Comparative Example 1

[0082] (1) Preparation of graphite materials:

[0083] Graphite precursors were obtained by crushing, acid washing, drying, and spheroidizing flake graphite. The graphite precursors and heavy oil filler were mixed evenly at a ratio of 100:25 and processed using a cold isostatic pressing device at 100 MPa to obtain graphite core precursors. The graphite core precursors were sintered at 1200℃ for 6 hours while being protected with N2 to obtain a second precursor. The second precursors were then shaped by ball milling at a speed of 200 r / min for 3 hours to eliminate the morphological changes caused by cold isostatic pressing, resulting in spheroidal graphite material from irregular particles.

[0084] Comparative Example 2

[0085] (1) Preparation of graphite materials:

[0086] After crushing, acid washing, drying and spheroidizing the flake graphite, a graphite precursor is obtained. The graphite precursor, coating agent 1 phenolic resin and coating agent 2 asphalt are mixed in a ratio of 100:10:2.5 and sintered at 1200℃ for 4 hours under N2 protection. After sieving and demagnetizing, the graphite material is obtained.

[0087] Comparative Example 3

[0088] (1) Preparation of graphite materials:

[0089] Graphite precursors were obtained by crushing, acid washing, drying, and spheroidizing flake graphite. The graphite precursors and heavy oil filler were mixed evenly at a ratio of 100:15 and processed using a cold isostatic pressing device at 100 MPa to obtain graphite core precursors. The graphite core precursors were sintered at 1200℃ for 6 hours while being protected with N2 to obtain a second precursor. The second precursors were then shaped by ball milling at a speed of 200 r / min for 3 hours to eliminate the morphological changes caused by cold isostatic pressing, resulting in spheroidal graphite material from irregular particles.

[0090] Comparative Example 4

[0091] (1) Preparation of graphite materials:

[0092] The graphite precursor was obtained by crushing, acid washing, drying and spheroidizing the flake graphite. The graphite precursor, coating agent 1 phenolic resin and coating agent 2 asphalt were mixed in a ratio of 100:10:1.5 and sintered at 1200℃ for 4 hours under N2 protection. After sieving and demagnetization, the graphite material was obtained.

[0093] Test method:

[0094] -10℃ 2C / 0.2C rate discharge capacity ratio test:

[0095] At room temperature, the battery is charged to 3.8V using a 1C constant current and constant voltage CCCV method. The battery is then placed at -10℃ for 6 hours and discharged at 0.2C to 1.9V. The discharge capacity is recorded. The battery is then removed and placed at 25℃ for 6 hours, followed by a 1C constant current and constant voltage CCCV charge to 3.8V. The battery is then placed at -10℃ for 6 hours and discharged at 2C to 1.9V. The discharge capacity is recorded. The 2C / 0.2C rate discharge capacity ratio at -10℃ is calculated.

[0096] -10℃ charging DCIR test:

[0097] The battery was left at -10℃ for 6 hours. The voltage E1 before the discharge started was recorded. The battery was charged at a constant current of 1C for 10 seconds. The upper limit voltage was 3.8V. The voltage E2 at this time was recorded. The charging DCIR at -10℃ was calculated by the formula (E2-E1) / 1C.

[0098] 45℃ cycle capacity retention:

[0099] The battery was placed in a 45℃ ambient chamber for 4 hours, charged at 1C constant current and constant voltage to 3.8V, cut off at 0.05C, placed for 30 minutes, and then discharged at 1C constant current to 2.0V. The 1C discharge capacity was recorded. After placing for 30 minutes, the cycle was repeated 300 times, and the discharge capacity after 300 cycles was recorded. The 45℃ cycle capacity retention rate was obtained as (discharge capacity after 300 cycles / 1C discharge capacity) × 100%.

[0100] Capacity recovery rate after 2 months of storage at 60℃:

[0101] The battery was charged to 3.8V using a 1C constant current constant voltage CCCV method, with a cutoff current of 0.05C. After resting for 30 minutes, it was discharged to 2V using a 1C constant current method, yielding the initial 1C discharge capacity. The battery was then stored in a 60℃ high-temperature chamber for 2 months, then left at room temperature for 4 hours, and then discharged to 2V using a 1C constant current method. After resting for 30 minutes, it was charged to 3.8V using a 1C constant current constant voltage CCCV method, with a cutoff current of 0.05C. After resting for 30 minutes, it was discharged to 2V using a 1C constant current method, yielding the recovered capacity. The capacity recovery rate after 2 months of storage at 60℃ was obtained by dividing the recovered capacity by the initial 1C discharge capacity (before storage).

[0102] In summary, the test results from Examples 1-14 and Comparative Examples 1-4 show that internal filling and external coating of graphite materials can optimize the internal porosity and external structure of graphite materials, reduce the probability of side reactions, thereby improving the low-temperature discharge ratio of the battery, reducing the low-temperature resistance of the battery, improving the high-temperature cycle retention rate of the battery, and the storage capacity recovery rate; comparing Examples 1-12 and Examples 13-14, the graphite material satisfies 0.15≤BET*(I D / I G With an OI ≤ 0.4, the low-temperature rate performance, high-temperature storage performance, and cycle performance of the battery can be further improved.

[0103] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

[0104] Table 1. Parameter settings for each embodiment and comparative example.

[0105] Table 2. Test results for each embodiment and comparative example.

Claims

1. A graphite material, wherein, The graphite material includes a graphite core and a coating layer, wherein the graphite core is filled with a filler.

2. The graphite material according to claim 1, wherein, The filler includes one or more of asphalt, coal tar, and heavy oil, and / or the coating layer includes one or more of asphalt, hard carbon, heavy oil, glucose, starch, and resin.

3. The graphite material according to claim 1 or 2, wherein, The coating layer comprises at least two coating structures.

4. The graphite material according to claim 3, wherein, The coating layer includes an inner coating structure close to the graphite core and an outer coating structure away from the graphite core, wherein the material of the inner coating structure is the same as the material of the filler.

5. The graphite material according to any one of claims 1-4, wherein, The graphite material satisfies: 0.15 ≤ BET*(I D / I G ) / OI≤0.4, where BET is the specific surface area of ​​the graphite material, I D / I G OI is the ratio of the intensity of the D peak and the G peak in the Raman spectrum of the graphite material, and OI is the ratio of the intensity of the (004) and (110) crystal plane diffraction peaks of the graphite material.

6. The graphite material according to claim 5, wherein, The BET is 1.5m 2 / g~5.0m 2 / g; and / or, the I D / I G The value is 0.1 to 0.5; and / or the OI is 2 to 5.

7. The graphite material according to claim 5 or 6, wherein, The electrochemically active area of ​​the graphite material is 1.5 m². 2 / g~3.0m 2 / g.

8. A method for preparing a graphite material as described in any one of claims 1-7, wherein, Includes the following steps: A graphite precursor and the filler are mixed and treated to obtain a graphite core precursor; the graphite core precursor is subjected to a first high-temperature treatment to obtain the graphite core; The graphite core and coating agent are mixed and subjected to a second high-temperature treatment to obtain the graphite material.

9. The method for preparing graphite material according to claim 8, wherein, The step of subjecting the graphite core precursor to a first high-temperature treatment to obtain the graphite core further includes grinding the graphite core.

10. The method for preparing graphite material according to claim 8 or 9, wherein, The graphite precursor includes one or more of artificial graphite and natural graphite.

11. The method for preparing the graphite material according to any one of claims 8-10, wherein, The mass ratio of the graphite precursor to the filler is 100:(10-40); and / or the mass ratio of the graphite core to the coating agent is 100:(3-40).

12. The method for preparing graphite material according to any one of claims 8-11, wherein, The temperature of the first high-temperature treatment is 900℃~1500℃; and / or the time of the first high-temperature treatment is 2h~6h; and / or the temperature of the second high-temperature treatment is 900℃~1500℃; and / or the time of the second high-temperature treatment is 2h~6h.

13. The method for preparing graphite material according to claim 9, wherein, The grinding process includes ball milling, the ball milling speed is 100 rpm to 800 rpm, and the ball milling time is 2 h to 8 h.

14. A negative electrode, wherein, The graphite material includes the graphite material according to any one of claims 1 to 7 or the graphite material prepared by the method according to any one of claims 8 to 13.

15. A battery, wherein, Includes the negative electrode sheet as described in claim 14.

16. An electrical appliance, wherein, Includes the battery as described in claim 15.

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